1. Technical Field
This invention relates generally to an apparatus for preventing the loss of a portion of a down-hole motor if the power section rotates a portion of the motor housing and, in particular, to an apparatus for discontinuing or severely restricting the flow of drilling fluid to a down-hole motor in response to rotation of a potion of the motor housing.
2. Description of the Related Art
In the field of oil well drilling, it is often desirable to use down-hole tools that are rotatable relative to the major portion of the drill string. For example, in some wells, such as horizontally drilled wells, it is desirable that a down-hole motor rotate just the drill bit, rather than having a larger surface motor rotate the entire drill string. Accordingly, it should be readily appreciated that some type of bearing is positioned in the down-hole tool so that the down-hole tool is freely rotatable relative to the drill string.
However, the environment to which such down-hole motors are subjected is extremely hostile. For example, the motor and bearing arrangement is continuously exposed to very high temperatures over very long periods of time with large amounts of debris passing therethrough. Accordingly, it is common for the bearings to occasionally fail. The failed bearings prevent free rotation of the drill bit relative to the motor housing; however, the operators of the drilling operation are ordinarily unaware of such failure and continue to pump drilling fluid through the down-hole motor.
Thus, the continued rotational force applied to the drill bit by the down-hole motor power section has a tendency to rotate the portion of the motor housing below the power section. Rotation of these sections of the down hole motor housing eventually results in at least one of the sections and the drill bit being unscrewed and separated from the remainder of the down-hole motor housing and possibly being lost in the well bore.
Once the motor housing and bit are lost in the well bore, time consuming and expensive "fishing" operations are necessary to attempt to retrieve the lost items. Often these relatively expensive items cannot be retrieved and continue to impede further drilling operations.
It has been suggested that undesirable rotation of the down-hole motor housing can be avoided by threadably attaching the down-hole motor housing to the lower portion of the drill string with left hand threads. Thus, when the down-hole motor applies a rotating force to its own housing, the joint is actually tightened rather than loosened. However, left hand threads have the inherent drawback of being loosened during normal operation. For example, during rotation of the entire drill string, the motor housing engages the subsurface strata and resists likewise rotation, thereby unscrewing the left hand threaded joint with attendant separation.
The present invention is directed to overcoming or minimizing one or more of the problems discussed above.